Apparatus for detecting a ferromagnetic object located on or in a person being screened comprises a first magnetic sensor which in use measures an ambient magnetic field or gradient within a first volume of space and produces a corresponding measurement signal, a primary power supply which provides power to the magnetic sensor, a signal processing circuit arranged in communication with the magnetic sensors configured to identify temporal variations in the measurement signal and from the identified temporal variations provide an output signal indicative of the presence of a ferromagnetic object within the volume of space, and a warning device operable by the output from the signal processing circuit to provide within the vicinity the apparatus at least one of an audible and a visible warning in response to the output signal from the signal processing circuit. The apparatus include a user operable input means which enables the warning device to be disabled by a user without powering down the magnetic sensors.
